With the recent, unprecedented success of the hydraulic fracturing and horizontal drilling in shale and tight rock formations, the natural gas production has increased exponentially. Raw natural gas typically consists primarily of methane. It also contains varying amounts of heavier hydrocarbons such as ethane, propane, butanes, pentanes and even higher molecular weight hydrocarbons. All these heavier hydrocarbons in raw natural gas are collectively referred to as natural gas liquid.
The rapid growth in hydraulic fracturing has resulted in a surge in production of natural gas liquid. Availability of low-cost ethane and propane has allowed new petrochemical investments in ethylene crackers and propane dehydrogenation plants in the US and elsewhere for polymer and chemicals production. The increased surplus volumes of propane, butanes, pentanes and hexanes, however, has exceeded the demand of these materials in industry, and thus created a need for a new hydrocarbon conversion process to convert these low value materials into higher value products.
Dehydrogenation processes to convert propane to propylene and isobutane to isobutylene (2-methylpropene) have been practiced before. Several commercial processes, such as CATOFIN® Dehydrogenation offered by CBI, Oleflex™ Technology by UOP and STAR Process® by ThyssenKrupp Industrial Solutions, are practiced in the industry, and high purity olefin products (99%+ purity) are produced for polymer or petrochemical applications. Dehydrogenating is limited by thermodynamic equilibrium, and the conversion per pass is typically less than 50%. The boiling point difference between the paraffin and olefin molecules after the dehydrogenating is very small and their separation is very difficult. In order to obtain the high purity olefin from the dehydrogenation reaction product mixture, the conventional dehydrogenation processes use a multi-stage paraffin/olefin splitter (e.g., multiple distillation columns). These olefin/paraffin separations are very energy intensive and costly.
Improved processes and equipment are needed for upgrading of natural gas liquid into valuable alkylate products.